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(Amended by Ord. No. 182,850, Eff. 1/3/14.)
91.2306.2. Wood-Frame Diaphragms. (Amended by Ord. No. 185,587, Eff. 7/16/18.) Wood-frame diaphragms shall be designed and constructed in accordance with AWC SDPWS. Where panels are fastened to framing members with staples, requirements and limitations of AWC DPWS shall be met and the allowable shear values set forth in CBC Table 2306.2(1) or 2306.2(2) shall only be permitted for structures assigned to Seismic Design Category A, B or C.
EXCEPTION: Allowable shear values where panels are fastened to framing members with staples may be used if such values are substantiated by cyclic testing and approved by the building official.
The allowable shear values of CBC Tables 2306.2(1) and 2306.2(2) are permitted to be increased 40% for wind design.
Wood structural panel diaphragms used to resist seismic forces in structures assigned to Seismic Design Category D, E or F shall be applied directly to the framing members.
EXCEPTION: Wood structural panel diaphragm is permitted to be fastened over solid lumber planking or laminated decking, provided the panel joints and lumber planking or laminated decking joints do not coincide.
91.2306.3. Wood-Frame Shear Walls. (Amended by Ord. No. 186,488, Eff. 12/27/19.) Wood-frame shear walls shall be designed and constructed in accordance with AWC SDPWS. For structures assigned to Seismic Design Category D, E, or F, application of Tables 4.3A and 4.3B of AWC SDPWS shall include the following:
1. Wood structural panel thickness for shear walls shall not be less than 3/8 inch (9.525 mm) thick, and studs shall not be spaced at more than 16 inches (406.4 mm) on center.
2. The maximum nominal unit shear capacities for three-ply plywood resisting seismic forces in structures assigned to Seismic Design Category D, E or F is 400 pounds per linear foot (plf) (181.43 kg per meter).
3. Where shear design values using allowable stress design (ASD) exceed 350 plf or load and resistance factor design (LRFD) exceed 500 plf, all framing members receiving edge nailing from abutting panels shall not be less than a single 3 inch (76.19 mm) nominal member, or two 2 inch (50.8 mm) nominal members fastened together in accordance with CBC Section 2306.1 to transfer the design shear value between framing members. Wood structural panel joint and sill plate nailing shall be staggered at all panel edges. See Sections 4.3.6.1 and 4.3.6.4.3 of AWC SDPWS for sill plate size and anchorage requirements.
4. Nails shall be placed not less than 1/2 inch (12.7 mm) in from the panel edges and not less than 3/8 inch (9.525 mm) from the edge of the connecting members for shear greater than 350 plf using ASD or 500 plf using LRFD. Nails shall be placed not less than 3/8 inch (9.525 mm) from panel edges and not less than 1/4 inch (6.35 mm) from the edge of the connecting members for shears of 350 plf or less using ASD or 500 plf or less using LRFD.
5. Table 4.3B of AWC SDPWS application is not allowed for structures assigned to Seismic design category D, E or F.
For structures assigned to Seismic Design Category D, Application of Table 4.3C of AWC SDPWS shall not be used below the top level in a multi-level building for structures.
Where panels are fastened to framing members with staples, requirements and limitations of AWC SDPWS shall be met and the allowable shear values set forth in CBC Tables 2306.3(1), 2306.3(2) or 2306.3(3) shall only be permitted for structures assigned to Seismic Design Category A, B or C.
EXCEPTION: Where panels are fastened to framing members with staples, allowable shear values may be used if such values are substantiated by cyclic testing and approved by the Superintendent of Building.
The allowable shear values in CBC Tables 2306.3(1) and 2306.3(2) are permitted to be increased 40% for wind design. Panels complying with ANSI/APA PRP-210 shall be permitted to use design values for Plywood Siding in the AWC SDPWS.
91.2306.4. Shear Walls Sheathed with Other Materials. Sheer walls sheathed with Portland cement plaster, gypsum lath, gypsum sheathing or gypsum board shall be designed and constructed in accordance with AWC SDPWS. Shear walls sheathed with these materials are permitted to resist horizontal forces using the allowable shear capacities set forth in CBC Table 2306.3(3). Shear walls sheathed with Portland cement plaster, gypsum lath, gypsum sheathing or gypsum board shall not be used to resist seismic forces in structures assigned to Seismic Design Category E or F. (Amended by Ord. No. 186,488, Eff. 12/27/19.)
Shear walls sheathed with lath, plaster or gypsum board shall not be used below the top level in a multi-level building for structures assigned to Seismic Design Category D.
(Amended by Ord. No. 185,587, Eff. 7/16/18.)
Section 2308 of the CBC is adopted by reference, except Sections 2308.6.1, 2308.6.5.1, 2308.6.5.2, 2308.6.8.1, 2308.6.9, 2308.6.10.2 and Table 2308.6.1 are not adopted; and, in lieu, LAMC Subdivisions and Paragraphs 91.2308.6.1, 91.2308.6.5.1, 91.2308.6.5.2, 91.2308.6.8.1, 91.2308.6.9, 91.2308.6.10.2, and LAMC Table 2308.6.1 are added.
91.2308.6.1. Braced Wall Lines. For the purpose of determining the amount and location of bracing required along each story level of a building, braced wall lines shall be designated as straight lines through the building plan in both the longitudinal and traverse direction and placed in accordance with LAMC Table 2308.6.1 and CBC Figure 2308.6.1. Braced wall line spacing shall not exceed the distance specified in LAMC Table 2308.6.1. In structures assigned to Seismic Design Category D or E, braced wall lines shall intersect perpendicularly to each other.
Wall framing to which sheathing used for bracing is applied shall be nominal 2 inch wide [actual 1-1/2 inch (38 mm)] or larger members. Braced wall panel construction types shall not be mixed within a braced wall line. Braced wall panels required by LAMC Section 91.2308.6.1 may be eliminated when all of the following requirements are met:
1. One story detached Group U occupancies are not more than 25 feet (7.62 m) in depth or length.
2. The roof and three enclosing walls are solid sheathed with 1/2 inch (12.7 mm) nominal thickness wood structural panels with 8d common nails placed 3/8 inches (9.525 mm) from panel edges and spaced not more than 6 inches (152.4 mm) on center along all panel edges and 12 inches (304.8 mm) on center along intermediate framing members. Wall openings for doors or windows are permitted provided a minimum 4 foot (1219.2 mm) wide wood structural braced panel with a minimum height to length ratio of 2 to 1 is provided at each end of the wall line and that the wall line be sheathed for 50% of its length.
Cripple walls bracing in Seismic Design Categories D and E shall be constructed in accordance with CBC Section 2308.6.6.2.
SEISMIC DESIGN CATEGORY | STORY CONDITION (SEE SECTION 2308.2) | MAXIMUM SPACING OF BRACED WALL LINES | BRACED PANEL LOCATION, SPACING (O.C.) AND MINIMUM PERCENTAGE (X) | MAXIMUM DISTANCE OF BRACED WALL PANELS FROM EACH END OF BRACED WALL LINE | ||
Bracing method b | ||||||
LIB | DWB, WSP | SFB, PBS, PCP, HPS, Gb c,d | ||||
SEISMIC DESIGN CATEGORY | STORY CONDITION (SEE SECTION 2308.2) | MAXIMUM SPACING OF BRACED WALL LINES | BRACED PANEL LOCATION, SPACING (O.C.) AND MINIMUM PERCENTAGE (X) | MAXIMUM DISTANCE OF BRACED WALL PANELS FROM EACH END OF BRACED WALL LINE | ||
Bracing method b | ||||||
LIB | DWB, WSP | SFB, PBS, PCP, HPS, Gb c,d | ||||
A and B |  | 35'-0" | Each end and ≤ 25'-0" o.c. | Each end and ≤ 25'-0" o.c. | Each end and ≤ 25'-0" o.c. | 12'-6" |
 | 35'-0" | Each end and ≤ 25'-0" o.c. | Each end and ≤ 25'-0" o.c. | Each end and ≤ 25'-0" o.c. | 12'-6" | |
 | 35'-0" | NP | Each end and ≤ 25'-0" o.c. | Each end and ≤ 25'-0" o.c. | 12'-6" | |
c |  | 35'-0" | NP | Each end and ≤ 25'-0" o.c. | Each end and ≤ 25'-0" o.c. | 12'-6" |
 | 35'-0" | NP | Each end and ≤ 25'-0" o.c. (minimum 25% of wall length)e | Each end and ≤ 25'-0" o.c. (minimum 25% of wall length)e | 12'-6" | |
D and E |  | 25'-0" | NP | SDS < 0.50: Each end and 25'-0" o.c. (minimum 21% of wall length)e,f,g,h | SDS < 0.50: Each end and 25'-0" o.c. (minimum 43% of wall length)e,f,g,h | 8'-0" |
0.50 ≤ SDS < 0.75: Each end and 25'-0" o.c. (minimum 32% of wall length)e,f,g,h | 0.50 ≤ SDS < 0.75: Each end and 25'-0" o.c. (minimum 59% of wall length)e,f,g,h | |||||
0.75 ≤ SDS 1.00: Each end and 25'-0" o.c. (minimum 37% of wall length)e,f,g,h | 0.75 ≤ SDS 1.00: Each end and 25'-0" o.c. (minimum 75% of wall length)e,f,g,h | |||||
SDS > 1.00: Each end and 25'-0" o.c. (minimum 48% of wall length)e,f,g,h | SDS > 1.00: Each end and 25'-0" o.c. (minimum 100% of wall length)e,f,g,h | |||||
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
NP = Not Permitted.
a. This table specifies minimum requirements for braced wall panels along interior or exterior braced wall lines.
b. See Section 2308.6.3 for full description of bracing methods.
c. For Method GB, gypsum wallboard applied to framing supports that are spaced at 16 inches on center.
d. The required lengths shall be doubled for gypsum board applied to only one face of a braced wall panel.
e. Percentage shown represents the minimum amount of bracing required along the building length (or wall length if the structure has an irregular shape).
f. Minimum length of panel bracing of one face of the wall for WSP sheathing shall be at least 4'-0" long or both feces of the wall for GB sheathing shall be at least 8'-0" long; h/w ratio shall not exceed 2:1. For WSP panel bracing of the same material on two faces of the wall, the minimum length is permitted to be one-half of the tabulated value, but the h/w ratio shall not exceed 2:1 and design for uplift is required. The 2:1 h/w ratio limitation does not apply to alternate braced wall panels constructed in accordance with Section 2308.6.5.1 or 2308.6.5.2.
g. Nailing as specified below shall occur at all panel edges at studs, at top and bottom plates and, where occurring, at blocking:
For 1/2-inch gypsum board, 5d (0.113-inch diameter) cooler nails at 7 inches on center;
For 5/8-inch gypsum board, No. 11 gage (0.120-inch diameter) at 7 inches on center;
For gypsum sheathing board, l-3/4 inches long by 7/l6-inch head, diamond point galvanized nails at 4 inches on center;
For gypsum lath, No. 13 gage (0.092 inch) by l-1/8 inches long, 19/64-inch head, plasterboard at 5 inches on center; and
For Portland cement plaster, No. 11 gage (0.120 inch) by 1-1/2 inches long, 7/l6-inch head at 6 inches on center.
h. WSP sheathing shall be a minimum of 15/32" thick nailed with 8d common placed 3/8 inch from panel edges and spaced not more than 6 inches on center and 12 inches on center along intermediate framing members.
91.2308.6.5.1. Alternate Braced Wall (ABW). (Amended by Ord. No. 187,719, Eff. 1/23/23.) An ABW shall be constructed in accordance with this Section and CBC Figure 2308.6.5.1. In one-story buildings, each panel shall have a length of not less than 2 feet 8 inches (813 mm) and a height of not more than 10 feet (3048 mm). Each panel shall be sheathed on one face with 15/32 inch (11.9 mm) minimum-thickness wood structural panel sheathing nailed with 8d common or galvanized box nails in accordance with CBC Table 2304.10.2 and blocked at wood structural panel edges. Two anchor bolts installed in accordance with CBC Section 2308.3.1 shall be provided in each panel. Anchor bolts shall be placed at each panel outside quarter points. Each panel end stud shall have a hold-down device fastened to the foundation, capable of providing an approved uplift capacity of not less than 1,800 pounds (8006 N). The hold-down device shall be installed in accordance with the manufacturer's recommendations. The ABW shall be supported directly on a foundation, or on floor framing supported directly on a foundation that is continuous across the entire length of the braced wall line. This foundation shall be reinforced with not less than one No. 4 bar top and bottom. Where the continuous foundation is required to have a depth greater than 12 inches (305 mm), a minimum 12 inch by 12 inch (305 mm by 305 mm) continuous footing or turned-down slab edge is permitted at door openings in the braced wall line. This continuous footing or turned-down slab edge shall be reinforced with not less than one No. 4 bar top and bottom. This reinforcement shall be lapped 15 inches (381 mm) with the reinforcement required in the continuous foundation located directly under the braced wall line.
Where the ABW is installed at the first story of a two-story building, the wood structural panel sheathing shall be provided on both faces, three anchor bolts shall be placed at one-quarter points, and tie-down device uplift capacity shall be not less than 3,000 pounds (13 344 N).
In one-story buildings, each panel shall have a length of not less than 16 inches (406 mm) and a height of not more than 10 feet (3048 mm). Each panel shall be sheathed on one face with a single layer of 15/32 inch (11.9 mm) minimum-thickness wood structural panel sheathing nailed with 8d common or galvanized box nails in accordance with CBC Figure 2308.6.5.2. The wood structural pane sheathing shall extend up over the solid sawn or glued-laminated header and shall be nailed in accordance with CBC Figure 2308.6.5.2. A built-up header consisting of at least two 2 inch by 12 inch (51 mm by 305 mm) boards, fastened in accordance with Item 24 of CBC Table 2304.10.2 shall be permitted to be used. A spacer, if used, shall be placed on the side of the built-up beam opposite the wood structural panel sheathing. The header shall extend between the inside faces of the first full-length outer studs of each panel. The clear span of the header between the inner studs of each panel shall be not less than 6 feet (1829 mm) and not more than 18 feet (5486 mm) in length. A strap with an uplift capacity of not less than 1,000 pounds (4400 N) shall fasten the header to the inner studs opposite the sheathing. One anchor bolt not less than 5/8 inch (15.9 mm) in diameter and installed in accordance with CBC Section 2308.3.1 shall be provided in the center of each sill plate. The studs at each end of the panel shall have a hold-down device fastened to the foundation with an uplift capacity of not less than 3,500 pounds (15 570 N).
Where a panel is located on one side of the opening, the header shall extend between the inside face of the first full-length stud of the panel and the bearing studs at the other end of the opening. A strap with an uplift capacity of not less than 1,000 pounds (4400 N) shall fasten the header to the bearing studs. The bearing studs shall also have a hold-down device fastened to the foundation with an uplift capacity of not less than 1,000 pounds (4400 N). The hold-down devices shall be an embedded strap type, installed in accordance with the manufacturer's recommendations. The PFH panels shall be supported directly on a foundation that is continuous across the entire length of the braced wall line. This foundation shall be reinforced with not less than one No. 4 bar top and bottom. Where the continuous foundation is required to have a depth greater than 12 inches (305 mm), a minimum 12 inch by 12 inch (305 mm by 305 mm) continuous footing or turned-down slab edge is permitted at door openings in the braced wall line. This continuous footing or turned-down slab edge shall be reinforced with not less than one No. 4 bar top and bottom. This reinforcement shall be lapped not less than 15 inches (381 mm) with the reinforcement required in the continuous foundation located directly under the braced wall line.
Where a PFH is installed at the first story of a two-story building, each panel shall have a length of not less than 24 inches (610 mm).
EXCEPTION: For structures with a maximum plan dimension not over 50 feet (15.24 m), continuous foundations are required at exterior walls only for structures not assigned to Seismic Design Category D, E or F.
For structures in Seismic Design Categories D and E, exterior braced wall panels shall be in the same plane vertically with the foundation or the portion of the structure containing the offset shall be designed in accordance with accepted engineering practice and CBC Section 2308.1.1.
EXCEPTIONS:
1. Exterior braced wall panels shall be permitted to be located not more than 4 feet (1219 mm) from the foundation below where supported by a floor constructed in accordance with all of the following:
1.1. Cantilevers or setbacks shall not exceed four times the nominal depth of the floor joists.
1.2. Floor joists shall be 2 inches by 10 inches (51 mm by 254 mm) or larger, and spaced not more than 16 inches (406 mm) on center.
1.3. The ratio of the back span to the cantilever shall be not less than 2 to 1.
1.4. Floor joists at ends of braced wall panels shall be doubled.
1.5. A continuous rim joist shall be connected to the ends of cantilevered joists. The rim joist is permitted to be spliced using a metal tie not less than 0.058 inch (1.47 mm) (16 galvanized gage) and 1-1/2 inches (38 mm) in width fastened with six 16d common nails on each side. The metal tie shall have a yield stress not less than 33,000 psi (227 MPa).
1.6. Joists at setbacks or the end of cantilevered joists shall not carry gravity loads from more than a single story having uniform wall and roof loads nor carry the reactions from headers having a span of 8 feet (2438 mm) or more.
2. The end of a required braced wall panel shall be allowed to extend not more than 1 foot (305 mm) over an opening in the wall below. This requirement is applicable to braced wall panels offset in plane and braced wall panels offset out of plane, as permitted by Exception 1. Braced wall panels are permitted to extend over an opening not more than 8 feet (2438 mm) in width where the header is a 4 inch by 12 inch (102 mm by 305 mm) or larger member.
91.2308.6.9. Attachment of Sheathing. (Amended by Ord. No. 187,719, Eff. 1/23/23.) Fastening of braced wall panel sheathing shall not be less than that prescribed in LAMC Table 2308.6.1 and CBC Table 2304.10.2. Wall sheathing shall not be attached to framing members by adhesives.
Staple fasteners in CBC Table 2304.10.2 shall not be used to resist or transfer seismic forces in structures assigned to Seismic Design Category D, E, or F.
EXCEPTION: Staples may be used to resist or transfer seismic forces when the allowable shear values are substantiated by cyclic testing and approved by the Superintendent of Building.
All braced wall panels shall extend to the roof sheathing and shall be attached to parallel roof rafters or blocking above with framing clips (18 gauge minimum) spaced at maximum 24 inches (6096 mm) on center four 8d nails per leg (total 8d nails per clip). Braced wall panels shall be laterally braced at each top corner and at maximum 24 inch (6096 mm) intervals along the top plate of discontinuous vertical framing.
EXCEPTION: In structures assigned to Seismic Design Category D, stone and masonry veneer is permitted to be used in the first story above grade plane, provided the following criteria are met:
1. The type of brace in accordance with LAMC Subdivision 91.2308.6.1 shall be WSP, and the allowable shear capacity in accordance with LAMC Section 91.2306.3 shall be not less than 350 plf (5108 N/m).
2. The braced wall panels in the first story shall be located at each end of the braced wall line and not more than 25 feet (7620 mm) on center, and the total length of braced wall panels shall be not less than 45% of the braced wall line length.
3. Hold-down connectors shall be provided at the ends of braced walls for the first floor to foundation with an allowable capacity of 2,100 pounds (9341 N).
4. Cripple walls shall not be permitted.
5. Anchored masonry and stone wall veneer not exceeding 5 inches (127 mm) in thickness shall conform to the requirements of Division 14, Article 1, Chapter IX of the Los Angeles Municipal Code and shall not extend more than 5 feet (1524 mm) above the first-story finished floor.
(Division Amended by Ord. No. 179,324, Eff. 12/10/07, Oper. 1/1/08.)
Section
91.2400 Basic Provisions.
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